U.S. Pat. No. 4,337,197, issued June 29, 1982, discloses as antibacterial agents, 3-acylamino-2-oxo-1-azetidinyl sulfates. As intermediates for the preparation of these products, the reference discloses, inter alia, compounds having the formula ##STR3## wherein X.sub.1 is acyl and X.sub.2 and X.sub.3 are hydrogen or organic substituents including alkyl.